Objective: Hippocampal volume is reduced
in posttraumatic stress disorder (PTSD). In the present study, we sought to determine
whether volume loss is homogenously distributed or
confined to a certain part of the structure.

Method: Twenty-two adult outpatients
with PTSD (11 after prolonged prepubertal trauma
and 11 after single adult trauma) and 22 matched healthy subjects were scanned at the
National Institute of Mental Health using
high-resolution 3T magnetic resonance imaging between
September 2003 and August 2004. PTSD diagnosis was conferred using the Structured Clinical
Interview for DSM-IV. Volumes of whole, anterior, and
posterior hippocampus and subiculum were compared between groups.

Results: Total hippocampal volume was
lower in patients with PTSD (p = .02), with a
significant diagnosis by hippocampal-subregion
interaction (p = .02). Post hoc analysis revealed
significantly smaller posterior hippocampi in PTSD (p =
.006), with no difference in the volumes of anterior
hippocampus or subiculum. No volume differences were found between PTSD participants with
prolonged childhood abuse compared to single adult trauma exposure.

Conclusions: The posterior hippocampus
has been associated with storage, processing, and retrieval of spatiotemporal memories, central
to the protective function of fear conditioning.
Volume deficit in the posterior hippocampus may indicate malfunction in this faculty, leading to
the exaggerated conditioned fear response observed in PTSD.